KR101876179B1 - Weatherable polyvinylidene fluoride coated substrates - Google Patents

Abstract

The present invention relates to architectural substrates coated with polyvinylidene fluoride (PVDF) dispersion coatings which produce weatherable materials. For one particular application, there is a PVDF coating on the front sheet or back sheet of a solar module for capturing and using solar radiation. As the polyvinylidene fluoride coating is exposed to the environment, it provides chemical resistance, low water vapor permeability, electrical insulation and protects against ultraviolet rays.

Description

[0001] WEATHERABLE POLYVINYLIDENE FLUORIDE COATED SUBSTRATES [0002] FIELD OF THE INVENTION [0003] The present invention relates to weather resistant polyvinylidene fluoride-

The present invention relates to architectural substrates coated with polyvinylidene fluoride (PVDF) dispersion coatings which produce weatherable materials. For one particular application, there is a PVDF coating on a frontsheet or backsheet of a solar module for capturing and using solar radiation. As the polyvinylidene fluoride coating is exposed to the environment, the substrate provides chemical resistance, low water vapor transmission, electrical insulation and especially weather resistance from ultraviolet radiation.

Photovoltaic modules consist of solar cells and backsheet encapsulated in an external (front) glazing material, typically a protective transparent package (encapsulant). Solar cells are manufactured from materials including but not limited to silicon, cadmium indium selenide (CIS), cadmium indium gallium selenide (CIGS), quantum dots, which are known for solar collectors. The backsheet is exposed to the environment on the back side of the solar module. The main function of the back sheet is to provide low moisture permeability, dielectric insulation for electrical circuits, ultraviolet and oxygen barrier properties, which protects silicon wafers (photovoltaic cells) from degradation induced by reaction with moisture, oxygen or ultraviolet need.

The back sheet of the collector may be a metal such as steel or aluminum. More recently, however, polymeric materials have been used in backing sheets. These materials include polyvinyl fluoride (PVF) materials from DuPont (U.S. Patent No. 6,646,196); Both ionomer / nylon alloys (US Pat. No. 6,660,930) and polyethylene terephthalate (PET) have been used singly and in combination as the backsheet layer of solar modules. PET is a relatively inexpensive polymer with good moisture resistance, but is susceptible to degradation when exposed to environmental influences such as ultraviolet, infrared and ozone. For many backsheet structures, PET is protected using a PVF film that is hard, relatively light stable, and chemically resistant and unaffected by exposure to moisture for extended periods of time. However, PVF films are relatively expensive. The general structure of the solar backsheet is usually PVF / PET / PVF, PVF / PET / Al / PVF and PE / PET / PVF multilayer laminated films. However, this structure can be difficult due to the disadvantage of low adhesion of PVF to PET or other substrate. Adhesion is usually improved by treating the surface of the polymer through a high energy surface treatment such as a corona discharge or similar technique that treats the polymer surface with an adhesive and / or increases the adhesion of the PVF film.

Another problem is that the thickness of the PVF film is usually about 25 um. Since the PVF resin is much more expensive than the PET resin, the overall cost of the backsheet is closely related to the thickness of the fluoropolymer layer. The cost savings of photovoltaic modules are very important for the commercial success of this technology.

One alternative is to use polyvinylidene fluoride (PVDF) as the fluoropolymer in the backsheet composition, as described in WO 08 / 157,159. PVDF can further improve performance, processing and cost over existing technologies. The back sheet formed from polyvinylidene fluoride (PVDF), polyvinylidene fluoride copolymer and polyvinylidene fluoride blend can take advantage of the advantages of polyvinylidene fluoride properties and overcomes the problems of other materials can do. PVDF can be in the form of a solvent coating or a water-based coating.

Solvent-based fluoropolymer coatings useful for photovoltaic applications are described in U.S. Patent Application Nos. 2007/0154704, 2007/0166469, and 2008/0261037. These applications describe blends of fluoropolymers (PVF or PVDF) with small amounts of adhesive polymers containing functional groups or crosslinking groups. Solvents such as n-methyl pyrrolidone, acetone, propylene carbonate, methyl ethyl ketone and the like used in these applications for coating formation are water-miscible or highly water-soluble (hydrophilic). These solvents cause water uptake unless they are completely removed in the bake cycle, leading to coating failure.

The Applicant has therefore developed polyvinylidene fluoride dispersion coatings useful for architectural substrate applications, including PV backsheet or front sheet substrate, to address many of the problems of existing laminated and coated structures. A simple PVDF coating containing a hydrophobic solvent, a non-reactive miscible co-resin (preferably an acrylic hybrid resin) can be used to coat and protect a solar backing sheet or other construction substrate without the need for a crosslinking additive Do. Another advantage of the PVDF dispersion coating composition of the present invention is that the film preventing shrinkage and embrittlement of the PET film substrate can be dried only slightly at a high temperature (170 DEG C to 180 DEG C).

In addition, PVDF can be functionalized to provide adhesive benefits. This functionalized PVDF can be used without any acrylic hybrid resin and can be used in small quantities with a much larger amount of acrylic hybrid resin. In addition, the aqueous PVDF / acrylic interpenetrating network dispersion coating, as well as the PVDF / acrylic hybrid composition, may also be used to provide a fluoropolymer coating for a back sheet or other substrate of a solar cell.

The present invention

a. Transparent glazing external material;

b. A plurality of solar cells encapsulated and interconnected; And

c. A solar cell module comprising a backsheet with a substrate coated with a dispersion fluoropolymer composition, wherein one or both sides exposed to the environment comprise a mixture of polyvinylidene fluoride (PVDF) and non-functionalized acrylic, .

Further, the present invention relates to:

a. Transparent glazing external material;

b. A plurality of solar cells encapsulated and interconnected; And

c. Wherein the one or both sides exposed to the environment comprises a backsheet having a substrate coated with a dispersion-functionalized fluoropolymer composition.

The present invention relates to an architectural structure, wherein a fluoropolymer coating, preferably a PVDF coating, is applied to one or both sides of a substrate material, said coating formulation comprising a solvent-based or water-based dispersion Coating. PVDF can be functionalized to improve adhesion. The PVDF resin can be combined with other miscible compatibilizers to further reduce costs and provide better film forming methods.

As used herein, "solar module" refers to a structure of a solar cell circuit sealed in an environmentally friendly laminate. Solar modules can be combined to form a pre-wired, field-installable solar panel. The photovoltaic array consisting of any number of PV modules and panels is a complete power generating unit.

A "hydrophobic" latent solvent as used herein means a solvent having a solubility in water of less than 10% by weight at 25 占 폚.

The backsheet of the present invention contains at least one fluoropolymer layer or copolymer layer, wherein the fluoropolymer composition constitutes the outermost sheet exposed to the environment.

The term fluoropolymer has in its chain one or more monomers selected from among compounds containing vinyl groups that can be opened to enable a polymerization reaction and includes one or more fluorine atoms directly attached to the vinyl group Atoms, at least one fluoroalkyl group, or at least one fluoroalkoxy group. Examples of fluoromonomers include vinyl fluoride; Vinylidene fluoride (VDF); Trifluoroethylene (VF3); Chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; Tetrafluoroethylene (TFE); Hexafluoropropylene (HFP); Perfluoro (methyl vinyl) ether (PMVE), perfluoro (ethyl vinyl) ether (PEVE) and perfluoro (propyl vinyl) ether (PPVE); Perfluoro (1,3-dioxol); But are not limited to, perfluoro (2,2-dimethyl-1,3-dioxole) (PDD). Preferred fluoropolymers are homopolymers and copolymers of vinyl fluoride and / or vinylidene fluoride.

The most preferred fluoropolymer is a fluoropolymer that reacts with a latent solvent (a solvent that does not dissolve or substantially swell the fluoropolymer resin at room temperature, but solubilizes the fluoropolymer resin at high temperature). The most preferred examples of such fluoropolymers are PVDF and PVF.

In the following description, PVDF will be used as a preferred and representative example of the fluoropolymer, but it may be replaced by another fluoropolymer.

Each PVDF layer composition of the present invention may comprise a PVDF homopolymer, a PVDF copolymer, a PVDF terpolymer, or a PVDF-homopolymer / copolymer; Or a blend of one or more other polymers compatible with such PVDF (co) polymers. The PVDF copolymers and ternary copolymers of the present invention are polymers in which the total weight of all monomer units in the total weight of vinylidene fluoride units in the polymer is greater than 40%, more preferably greater than 70%. Copolymers, terpolymers and higher order polymers of vinylidene fluoride can be prepared by reacting vinylidene fluoride with at least one of vinyl fluoride, trifluoroethene, tetrafluoroethene, one or more partially or fully fluorinated alpha- Olefins such as 3,3,3-trifluoro-1-propene, 1,2,3,3,3-pentafluoropropene, 3,3,3,4,4-pentafluoro- -Butene and hexafluoropropene), partially fluorinated olefin hexafluoroisobutylene, perfluorinated vinyl ethers (e.g., perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, perfluoro-n-propyl Vinyl ether and perfluoro-2-propoxypropyl vinyl ether), fluorinated dioxols (such as perfluoro (1,3-dioxol) and perfluoro (2,2-dimethyl- ), Allyl-based, partially fluorinated allyl-based or fluorinated allyl-based monomers (e.g., 2-hydroxyethylallyl ether or 3- Oxy-propanediol) at least one monomer selected from the group consisting of; And ethene or propene. Preferred copolymers or terpolymers are formed by vinyl fluoride, trifluoroethene, tetrafluoroethene (TFE), and hexafluoropropene (HFP).

Particularly preferred copolymers include VDF copolymers containing about 71 to about 99 weight percent VDF and correspondingly about 1 to 29 weight percent HFP; A VDF copolymer comprising about 71 to about 99 weight percent VDF and correspondingly about 1 to about 29 weight percent TFE (e.g., as disclosed in U.S. Patent No. 3,178,399); And VDF comprising about 71 to 99 wt% of VDF and correspondingly about 1 to 29 wt% of trifluoroethylene.

Particularly preferred thermoplastic terpolymers include VDF, terpolymers of HFP and TFE, and ternary copolymers of VDF, trifluoroethene and TFE. These particularly preferred tertiary copolymers include VDF in an amount of at least 71 wt%, and the remaining other comonomers may be present in varying proportions, but the total constitutes less than 29 wt% of the terpolymer.

In one embodiment, it is useful that the melting point of the fluoropolymer exceeds 125 DEG C, more preferably above 140 DEG C, and most preferably above 150 DEG C, especially when the fluoropolymer is exposed to the hot working process .

In addition, PVDF can be grafted with a reactive monomer (e.g., maleic anhydride) and adhered to the surface to improve adhesion. These functionalized resins are described in U.S. Patent No. 7,241,817, which is incorporated herein by reference. These resins were used for the purpose of improving PVDF laminates and coating adhesion.

The PVDF layer may also be a blend of a PVDF polymer and a miscible polymer, such as, but not limited to, acrylic polymers or copolymers such as polymethylmethacrylate (PMMA), or MMA And acrylic monomers such as ethyl acrylate or butyl acrylate, wherein the PVDF occupies a proportion greater than 40% by weight. PVDF and PMMA can be melt blended to form a homogeneous blend. A preferred embodiment is a blend of 50-90 wt% PVDF and 10-50 wt% polymethyl methacrylate or polymethyl methacrylate copolymer, wherein 50-70 wt% PVDF and 10-30 wt% The ratio of PMMA mono- or co-polymer is preferred. Preferably, the acrylic polymer is nonfunctional, which means that the acrylic polymer does not contain reactive functional groups such as carboxylates, amines, anhydrides, isocyanates or epoxies. RTI ID = 0.0 > PVDF < / RTI > or a portion thereof. In order to improve the physical properties, a hybrid resin or PVDF may be crosslinked. In particular for copolymers with a low melting point (below 150 ° C), the use of crosslinking agents can improve the heat resistance of these coatings to future PV module lamination conditions (150 ° C, 5 minutes). In one embodiment, the functional PVDF and the non-functional acrylic polymer may be blended at a ratio of 10:90 to 90:10 to form a PVDF composition.

According to another embodiment of the present invention there is provided an aqueous dispersion of a polymer, which is substantially free or totally free of organic solvents (less than about 20% by weight, preferably less than about 10% by weight based on the total weight of the formulation) May be used. One example of such an aqueous composition is a fluoropolymer / acrylic hybrid dispersion (also known as an acryl-modified fluoropolymer ("AMF") dispersion). Common methods of making AMF dispersions are described in U.S. Patent No. 5,646,201, U.S. Patent No. 6,680,357, and U.S. Patent Application No. 61/078619, which are incorporated herein by reference. The AMF dispersion is formed by swelling a fluoropolymer seed dispersion into one or more acrylic monomers and then polymerizing the acrylic monomers. The AMF dispersion may be in the form of a hybrid interpenetrating network dispersion (an acrylic monomer that is compatible with an acrylic monomer or a fluoropolymer seed) or two or more different acrylic monomers (one or more of which is a fluoropolymer Which can not be miscible with the seed and therefore partly in the form of an interpenetrating network depending on the polymer).

In a preferred AMF embodiment of the present invention, a high melting point (mp > 125 deg. C, preferably greater than 140 deg. C and most preferably greater than 150 deg. C) with a nonfunctional acrylic polymer that can be miscible with the fluoropolymer component Fluoropolymer seeds are used. Examples of such miscible acrylic polymer compositions are provided in patent documents and patent applications incorporated herein by reference. In this embodiment, the morphology of the AMF dispersion particles may be of the "core-shell" or "IPN" type. Indeed, an IPN type dispersion based on a PVDF homopolymer or copolymer can be defined as a polymer having a first heat melting endotherm of less than about 20 J / g on a dry polymer. When a dispersion of the core-shell type is used in the present invention, it is possible to obtain a uniform coating of the fluoropolymer and the acrylic component at any point during the manufacturing process (during drying of the coating or during subsequent lamination or heat treatment steps) To a temperature within at least 10 [deg.] C of the crystallization melting point (or higher temperature) of the fluoropolymer component. In the case of using IPN-type dispersions, it is not necessary to heat the composition to a minimum film-forming temperature of the dispersion at any time (that is, the minimum temperature required to form the aqueous composition as a continuous-drying film).

A preferred second AMF embodiment is a thermally durable thermosetting adhesive composition comprising thermodynamically miscible acrylic components and having little or no crystallinity (crystallization melting point is less than 125 占 폚 and total crystallinity as measured by differential scanning calorimetry is 20 J / g) < / RTI > is formed from the PVDF copolymer seed. In this case, the material is likely to have an IPN-type shape, and it is not necessary to heat the composition at any time above the minimum film forming temperature of the dispersion (i.e., the minimum temperature required to form the aqueous composition into a continuous drying film) none. In this preferred second AMF embodiment, to improve heat resistance, the IPN may be internally crosslinked using reactive monomers incorporated therein, or may be prepared by adding a reactive hybrid resin that can be internally crosslinked, Heat resistance can be improved. In these cases, the reaction components are set not to react with the substrate. Generally, the ratio of the fluoropolymer seed to the acrylic monomer ranges from 10 parts by weight to 90 parts by weight of the fluoropolymer relative to 90 parts by weight to 10 parts by weight of acrylic, preferably from 50 to 20 parts by weight of fluoro 50 parts by weight to 80 parts by weight of the polymer. Another embodiment is a fluoropolymer / acrylic hybrid in which two or more different vinyl monomer compositions are sequentially polymerized in the presence of a fluoropolymeric seed as described in U.S. Provisional Patent Application No. 61/078619.

The fluoropolymer composition may include, in addition to PVDF, other additives such as impact modifiers, UV stabilizers, plasticizers, processing aids, fillers, colorants, pigments, antioxidants, antistatic agents, surfactants, toners, But are not limited thereto. Since ultraviolet resistance is the main function of the backing layer, the ultraviolet absorber is present in the PVDF and / or in the barrier layer at a level of from 0% to 10% by weight, preferably from 0.5% to 7.0% by weight. In one preferred embodiment, the pigment is added to the fluoropolymer composition for backcoating of the solar module to help reflect light back into the solar module while absorbing or blocking ultraviolet radiation transmitted. The pigment may be used at levels of from 0.5% to 50% by weight based on the polymer. In the case of a solar cell front sheet, a transparent coating containing 0 to 1% by weight of pigment is preferred. In one embodiment, the weather resistant fluoropolymer composition comprises 30 to 100 weight percent of a fluoropolymer; 0 to 70 wt% miscible resin (e.g., (meth) acrylic polymer or copolymer); 0 to 30% by weight of an inorganic filler or pigment; And 0 to 7% by weight of other additives.

To improve heat resistance, the fluoropolymer composition may contain from 2 to 33% of a low molecular weight crosslinking agent which crosslinks the fluoropolymer preparation. Examples of useful crosslinking agents are DESMODUR N3300, DESMODUR 4265 BL and CYMEL 300 and 303. The addition of a crosslinking agent improves the thermal stability, hardness, scratch resistance and even solvent resistance of the coating. According to one preferred embodiment, the fluoropolymer composition contains no cross-linking agent.

The PVDF composition is coated on the polymer backing substrate of the solar back sheet or front sheet. The backing layer is used to support the PVDF coating, and may also perform other functions such as a moisture barrier layer, and / or an insulating layer. The polymeric support layer may be a single layer, or it may have a multi-layer structure composed of two or more materials. Examples of support layers useful in the present invention include, but are not limited to, aluminum foils, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), functionalized polyolefins and their alloys, and ethylene vinyl alcohol. One preferred support layer is a PET layer substrate. The support layer substrate of the present invention has a thickness of 25 to 500 μm, preferably 50 to 250 μm, in sheet or film form. The substrate is usually formed by a known method such as a biaxial stretching and a heat setting process. In addition, the backsheet may have a fluoropolymer composition in the outermost layer and may comprise a multilayer further comprising at least one barrier layer selected from the group consisting of ethylene vinyl acetate, polyethylene terephthalate, polypropylene terephthalate, aluminum or reactive polyethylene Structure. In addition, the back sheet substrate is based on polyethylene terephthalate or polybutylene terephthalate.

A support layer, such as polyethylene terephthalate, which can perform the present invention as an untreated but still adherent support layer, can be formed by a method known in the art (for example, coating with a polymer primer, And / or treated with a plasma). In one preferred embodiment, the substrate is prime with a fluoropolymer, a hybrid resin, or a primer compatible with both. The hybrid resin in the primer used by the Applicant in the fluoropolymer composition was not intended to react with the primer on PET. The primer only improves the surface wettability, absorbency and interlayer diffusibility of the fluoro composition. The most preferred primer composition is an acrylic composition which provides good miscibility with the PVDF coating.

PET exhibits excellent moisture resistance at relatively low cost, but is susceptible to degradation when exposed to environmental influences such as ultraviolet, infrared and ozone. In the implementations presented below, PET is used as an exemplary support layer, but it is readily conceivable that one of ordinary skill in the art would be able to replace PET with other polymer support layers.

The PVDF-containing backsheet may be a single layer or multi-layer structure with a total thickness generally between 25 microns and 500 microns, preferably between 75 microns and 350 microns. In one embodiment, the backsheet is comprised of a 10 mil (250 um) barrier layer having on one or both sides a PVDF layer of 5 microns to 25 microns, preferably 10 microns to 20 microns.

The support layer may have a polyvinylidene fluoride layer on one or both sides. When the PDVF layer is provided on both sides of the barrier layer, although these layers may have different thicknesses and compositions, it is preferred that each side is the same composition to aid in manufacturing.

A preferred method of forming the polyvinylidene fluoride outer layer is coating with a solvent based or aqueous dispersion coating composition. The fluoropolymer coating can be applied to the surface treated PET layer by known methods (e.g., but not limited to, brushing, spraying, dipping, laserjet, etc.). The curing temperature of the solvent dispersion coating may range from 150 to 230 占 폚. The most preferred curing temperature of the PVDF solvent coating formulation is 150-180 占 폚. To prevent shrinkage and embrittlement of the PET film, a high curing temperature (above 180 ° C) should be avoided. In Example 17, a number of curing formulations in such a preferable temperature range are listed. Because there is a need for low bake temperatures, selecting a suitable solvent (e.g., boiling) is essential for successful formulation. Solvents with high boiling points may not be fully evaporated at low bake temperatures, and residual solvents may lead to coating failure.

In general, in order to form the fluoropolymer coating composition of the present invention, the dry PVDF is mixed with a hydrophobic solvent or a dry pigment (which may be pre-dispersed in a non-water-soluble solvent) with these solvents, Blend with a mixture of acrylic copolymer resins (which may be dissolved or added in a dry state). Thereafter, the mixture is mixed with a high shear mixer (e.g., using a Cowles dispersing element), milling balls, paint shaker agitation, or other methods known in the art Lt; / RTI > These and similar dispersion methods are well known to those skilled in the art of paint formulation.

Such a fluoropolymer dispersion composition is applied onto a suitable carrier / substrate sheet using either roll coating, spray coating, or doctor blade application. The coating thickness depends on the formulation viscosity, but may be adjusted so that the dry coating thickness is 10 to 50 μm, preferably 15 to 25 μm. Normally, the coating is baked and cured at 170 to 200 DEG C for 1 to 5 minutes. In a most preferred embodiment, the coating is baked at 170 to 180 占 폚 for 1 to 2 minutes.

The most preferred fluoropolymer compositions are non-aqueous dispersions, not solutions. Solvents used to prepare such dispersions are predominantly hydrophobic latent solvents for fluoropolymers, i.e., solvents which are good solvents for fluoropolymers at elevated temperatures (not normal temperatures). When an active solvent (a solvent that substantially dissolves PVDF at room temperature) is used, it is used as a co-solvent at 30% or less of the total solvent weight.

It is preferable to use a hydrophobic solvent (water solubility of less than 10% at 25 캜) because of potential adhesion failure when using a water-miscible solvent. If a small amount of solvent remains in the coating using a water-miscible solvent such as NMP, the coating will readily absorb water. This water uptake will lead to blistering and delamination of the coating, which will result in failure of the backsheet construction. The following table lists some solvents commonly used in coating formulations with their water solubilities.

In another embodiment of the present invention, the pure PVDF resin is blended with maleic anhydride grafted PVDF resin (MA-PVDF) to improve the overall adhesion of the coating. A coating obtained by mixing a combination of PVDF and MA-PVDF with other components and solvents as described above is applied and cured.

In another embodiment, the MA-PVDF resin may be pre-dissolved in an active solvent such as NMP prior to mixing with the remainder of the PVDF formulation. Although water-miscible NMP solvents can cause adhesion problems in pure PVDF coatings, the presence of such co-agents can be compensated for by the improved adhesion of the MA-PVDF resin. In such a blend, the total amount of NMP may be less than 30% of the total solvent composition.

According to another embodiment, a solution is formed with a pure MA-PVDF resin dissolved in an active solvent such as NMP, together with an acrylic copolymer resin and a pigment additive, to prepare a coating formulation. The use of water-miscible solvents can be compensated for by the improved adhesion of the MA-PVDF resin.

In addition to the fact that the fluoropolymer composition of the present invention is useful as a front sheet of a solar module as well as a coating for a back sheet, the coating composition can also be used for other architectural uses (e.g., glazing for construction, roofing ) And exterior wall construction (siding)).

Unless otherwise specified in the text, the percentages are percent by weight and the molecular weight is the weight average molecular weight.

Example

Example 1 - Organic solvent dispersion coating

The dispersion coating was formulated with PVDF homopolymer resin (emulsion polymer containing Mw 450K, Mn 130K, based on PMMA adjustment), and acrylic copolymer (PARALOID B44 from Rohm and Haas). The formulation of Table 2 was mixed with 125 grams of 4 mm glass beads in a paint shaker for 30 minutes. The coating thus obtained was applied to a prime-treated PET film. The coating was flash dried for 10 minutes at room temperature and then baked at 200 ° C (392 ° F) for 10 minutes. I got a smooth white coating. This coating was immersed in 100 F water for one week and exposed at 85 F / 85% relative humidity for 1000 hours, then cross-hatch adhesion (ASTM D3359). The coating passed the adhesion test successfully (see Table 17). In the D3359 test, the coating was cut into vertical sections with a special cutting tool to create 100 small squares. The tape was attached and then peeled off again to separate these squares. In this test, the number of squares removed by the tape was counted. If more than 20 (20%) squares are stripped, the coating is broken. If less than 20% of the square was peeled off, the coating was considered to have passed the adhesion test. This coating was exposed for 1000 hours at 85 캜, 85% relative humidity (damp heat exposure) and this test was used in the tests of the following examples.

Example 2 - Aqueous Dispersion Coating

According to the comparative example method of Table 1 described in U.S. Patent No. 6,680,357 (incorporated herein by reference), a non-reactive acrylic composition consisting of 66% methyl methacrylate, 31% ethyl acrylate, 3% methacrylic acid, An AMF dispersion was prepared using PVDF homopolymer (homopolymer: acrylic acid ratio = 70:30). The aqueous solution was neutralized with aqueous ammonia to a pH of about 8.0 to obtain a solids content of 37.7% by weight. The dispersion had a first heat DSC melting enthalpy of 32 J / g for the dry polymer and a broad crystallization melting peak in the range of 160-170 占 폚.

A white aqueous coating based on this dispersion was formulated using the following formulation.

The pigment concentrate was prepared using a Cowles high speed mixer (operated at 2000 rpm for 15 minutes and then at 4000 rpm for 30 minutes). The latex formulation was mixed for 10 minutes at 500 rpm using a low speed mixer.

The white aqueous coating was applied on the same pretreated PET as in Example 1 using a 5 mil draw down blade so that the dry coating thickness was about 1 mil. The thus obtained sample was flash-dried at room temperature for 10 minutes and then oven-baked at 180 ° C for 10 minutes. The sample was immersed in water at 85 캜 for 72 hours, and the coating adhesion was tested as in Example 1. Showed excellent adhesion maintaining 100% of the squares on the substrate as specified.

Example 3 (90:10 isophorone-cyclohexanone solvent blend)

PVDF-acrylic dispersion coatings were prepared using mixed solvent blends as described in Table 5 below. This is to prove that a mixture of latent solvents can be used for the dispersion coating. These solvents will not be considered as "active" solvents and will not significantly swell the PVDF resin at room temperature. The blend was prepared as described in Example 1 using isophorone and cyclohexanone as solvents (isophorone: cyclohexanone) in a ratio of 90:10. This formulation was coated onto a prime treated PET film (SKC SH22), evaporated at room temperature for 10 minutes, and then baked at 200 ° C for 10 minutes. After cooling, cross-hatch test on the coating showed 100% coating adhesion. Additional testing was performed by exposing the coated sheet to moisture (85%, 85 캜, Thermotron exposure unit). Compared to the simple immersion test, this type of moisture exposure is a more general performance test. After 1000 hours of exposure, the coating remained 100% adhesive (see Table 17).

Example 4 (80:20 isophorone-cyclohexanone solvent blend)

PVDF-acrylic dispersion coatings were prepared using blended solvent blends as described in Table 6 below. The blend was prepared as described in Example 1 using isophorone and cyclohexanone as solvents (isophorone: cyclohexanone) in a ratio of 80:20. This formulation was coated onto a prime treated PET film (SKC SH22), evaporated at room temperature for 10 minutes, and then baked at 200 ° C for 10 minutes. After cooling, cross-hatch test on the coating showed 100% coating adhesion. Additional testing was performed by exposing the coated sheet to moisture (85%, 85 캜, Thermotron exposure unit). Compared to the simple immersion test, this type of moisture exposure is a more general performance test. After 1000 hours of exposure, the coating remained 100% adhesive (see Table 17).

Example 5 (70:30 isophorone-cyclohexanone solvent blend)

PVDF-acrylic dispersion coatings were prepared using blended solvent blends as described in Table 7 below. The blend was prepared as described in Example 1 using isophorone and cyclohexanone as solvents (isophorone: cyclohexanone) in a ratio of 70:30. This formulation was coated onto a prime treated PET film (SKC SH22), evaporated at room temperature for 10 minutes, and then baked at 200 ° C for 10 minutes. After cooling, cross-hatch test on the coating showed 100% coating adhesion. Additional testing was performed by exposing the coated sheet to moisture (85%, 85 캜, Thermotron exposure unit). Compared to the simple immersion test, this type of moisture exposure is a more general performance test. After 1000 hours of exposure, the coating remained 100% adhesive (see Table 17).

Example 6 (50:50 isophorone-cyclohexanone solvent blend)

PVDF-acrylic dispersion coatings were prepared using blended solvent blends as described in Table 8 below. The blend was prepared as described in Example 1 using isophorone and cyclohexanone as a solvent in a ratio of 50:50 (isophorone: cyclohexanone). This formulation was coated onto a prime treated PET film (SKC SH22), evaporated at room temperature for 10 minutes, and then baked at 200 ° C for 10 minutes. After cooling, cross-hatch test on the coating showed 100% coating adhesion. Additional testing was performed by exposing the coated sheet to moisture (85%, 85 캜, Thermotron exposure unit). Compared to the simple immersion test, this type of moisture exposure is a more general performance test. After 1000 hours of exposure, the coating remained 100% adhesive (see Table 17).

Example 7 (30:70 isophorone-cyclohexanone solvent blend)

PVDF-acrylic dispersion coatings were prepared using blended solvent blends as described in Table 9 below. The blend was prepared as described in Example 1 using isophorone and cyclohexanone as solvents (isophorone: cyclohexanone) in a ratio of 30:70. This formulation was coated onto a prime treated PET film (SKC SH22), evaporated at room temperature for 10 minutes, and then baked at 200 ° C for 10 minutes. After cooling, cross-hatch test on the coating showed 100% coating adhesion. Additional testing was performed by exposing the coated sheet to moisture (85%, 85 캜, Thermotron exposure unit). Compared to the simple immersion test, this type of moisture exposure is a more general performance test. After 1000 hours of exposure, the coating remained 100% adhesive (see Table 17).

Example 8 (20:80 isophorone-cyclohexanone solvent blend)

PVDF-acrylic dispersion coatings were prepared using blended solvent blends as described in Table 10 below. The blend was prepared as described in Example 1 using isophorone and cyclohexanone as solvents (isophorone: cyclohexanone) in a ratio of 20:80. This formulation was coated onto a prime treated PET film (SKC SH22), evaporated at room temperature for 10 minutes, and then baked at 200 ° C for 10 minutes. After cooling, cross-hatch test on the coating showed 100% coating adhesion. Additional testing was performed by exposing the coated sheet to moisture (85%, 85 캜, Thermotron exposure unit). Compared to the simple immersion test, this type of moisture exposure is a more general performance test. After 1000 hours of exposure, the coating remained 100% adhesive (see Table 17).

Example 9 (10:90 isophorone-cyclohexanone solvent blend)

PVDF-acrylic dispersion coatings were prepared using blended solvent blends as described in Table 11 below. The blend was prepared as described in Example 1 using isophorone and cyclohexanone as solvents (isophorone: cyclohexanone) in a ratio of 10:90. This formulation was coated onto a prime treated PET film (SKC SH22), evaporated at room temperature for 10 minutes, and then baked at 200 ° C for 10 minutes. After cooling, cross-hatch test on the coating showed 100% coating adhesion. Additional testing was performed by exposing the coated sheet to moisture (85%, 85 캜, Thermotron exposure unit). Compared to the simple immersion test, this type of moisture exposure is a more general performance test. After 1000 hours of exposure, the coating remained 100% adhesive (see Table 17).

Example 10 Use of Alternative Acrylic Resins

In order to show that other commercially available PMMA-based acrylic resin is used in the present invention, the following formulation was prepared by the method in Example 1 and coated on a PET film. After baking, it became a smooth, flawless coating and passed a high humidity exposure test of 1000 hours without adhesive failure.

Example 11 (a maleic anhydride functional PVDF (KYNAR ADX) hybrid resin was used with a 90:10 isophorone / cyclohexanone solvent blend and B44 acrylic resin)

PVDF-acrylic dispersion coatings were prepared using blended solvent blends as described in Table 13 below. The blend was prepared as described in Example 1 using isophorone and cyclohexanone as solvents (isophorone: cyclohexanone) in a ratio of 90:10. This formulation was coated onto a prime treated PET film (SKC SH22), evaporated at room temperature for 10 minutes, and then baked at 200 ° C for 10 minutes. After cooling, cross-hatch test on the coating showed 100% coating adhesion. Additional testing was performed by exposing the coated sheet to moisture (85%, 85 캜, Thermotron exposure unit). Compared to the simple immersion test, this type of moisture exposure is a more general performance test. After 1000 hours of exposure, the coating remained 100% adhesive (see Table 17).

Example 12 (KYNAR ADX hybrid resin is used with 50:50 isophorone / cyclohexanone solvent blend and B44 acrylic resin)

PVDF-acrylic dispersion coatings were prepared using mixed solvent blends as described in Table 14 below. The blend was prepared as described in Example 1 using isophorone and cyclohexanone as a solvent in a ratio of 50:50 (isophorone: cyclohexanone). This formulation was coated onto a prime treated PET film (SKC SH22), evaporated at room temperature for 10 minutes, and then baked at 200 ° C for 10 minutes. After cooling, cross-hatch test on the coating showed 100% coating adhesion. Additional testing was performed by exposing the coated sheet to moisture (85%, 85 캜, Thermotron exposure unit). Compared to the simple immersion test, this type of moisture exposure is a more general performance test. After 1000 hours of exposure, the coating remained 100% adhesive (see Table 17).

Example 13 (KYNAR ADX functional PVDF hybrid resin is used with a 10:90 isophorone / cyclohexanone solvent blend and B44 acrylic resin)

PVDF-acrylic dispersion coatings were prepared using blended solvent blends as set forth in Table 15 below. The blend was prepared as described in Example 1 using isophorone and cyclohexanone as solvents (isophorone: cyclohexanone) in a ratio of 10:90. This formulation was coated onto a prime treated PET film (SKC SH22), evaporated at room temperature for 10 minutes, and then baked at 200 ° C for 10 minutes. After cooling, cross-hatch test on the coating showed 100% coating adhesion. Additional testing was performed by exposing the coated sheet to moisture (85%, 85 캜, Thermotron exposure unit). Compared to the simple immersion test, this type of moisture exposure is a more general performance test. After 1000 hours of exposure, the coating remained 100% adhesive (see Table 17).

Example 14 (KYNAR ADX functional PVDF hybrid resin was used with a 10:90 isophorone / cyclohexanone solvent blend and A-21 acrylic resin)

PVDF-acrylic dispersion coatings were prepared using blended solvent blends as set forth in Table 16 below. The blend was prepared as described in Example 1 using isophorone and cyclohexanone as solvents (isophorone: cyclohexanone) in a ratio of 10:90. This formulation was coated onto a prime treated PET film (SKC SH22), evaporated at room temperature for 10 minutes, and then baked at 200 ° C for 10 minutes. After cooling, cross-hatch test on the coating showed 100% coating adhesion. Additional testing was performed by exposing the coated sheet to moisture (85%, 85 캜, Thermotron exposure unit). Compared to the simple immersion test, this type of moisture exposure is a more general performance test. After 1000 hours of exposure, the coating remained 100% adhesive (see Table 17).

Example 15 Use of a functional PVDF resin solution for coating

In this embodiment, the acrylic resin and the pigment are added to the functional PVDF resin described in Examples 11 to 14, and the resin itself can be used as a solution (completely dissolved). In order to carry out the present embodiment, it is necessary to prepare a solution in which a functional PVDF resin is dissolved in an active solvent such as NMP or DMAC at a concentration of 10 to 30%, and to blend an appropriate amount of acrylic resin together with the pigment. Formulation examples are shown in Table 18 below.

The formulations were mixed using standard methods and equipment known to those skilled in the art. This application may also be accomplished by known processes such as draw down, roll coating, and / or doctor blade casting. The bake step was conducted at 190 to 200 DEG C for 4 to 8 minutes.

Example 16 Use of a functional PVDF resin solution combined with a dispersion formulation

In this example, the functional PVDF resins described above in Examples 11-14 can be used as solutions (fully dissolved) for blending with PVDF dispersion formulations, similar to Examples 11-14. This method is an alternative to blending a functionalized PVDF resin in a dry state with the dispersion formulation. In order to carry out the present embodiment, it is necessary to prepare a solution in which a functional PVDF resin is dissolved in an active solvent such as NMP or DMAC at a concentration of 10 to 30%, and to blend with a conventional dispersion preparation. Formulation examples are shown in Table 19 below.

This formulation was mixed using standard methods and equipment known to those skilled in the art. The application may be by known procedures such as stretching, roll coating, and / or doctor blade casting. The bake step was conducted at a temperature of 190 ° C to 200 ° C for 4 to 8 minutes.

Example 17 Low temperature baked aqueous dispersion coating using crosslinking

The PVDF-acrylic hybrid dispersion was prepared as follows: PVDF copolymer fluoropolymer latex (resin composition: 75/25 wt% VF2 / HFP, latex particle size 140nm by light scattering, 41 wt% solids) It was used as received. Was first heat DSC melting enthalpy is 17.5 J / g on the dried polymer dispersion of water, the main crystal melting peak at 103 ℃ the VAZO ^® with -67 (Dupont), POLYSTEP B7 ammonium lauryl sulfate (STEPAN, 30 wt. % Aqueous solution) was used as received. Methyl methacrylate, hydroxyethyl methacrylate, methacrylic acid and ethyl acrylate were used as received from Aldrich.

A monomer mixture (monomer mixture A) was prepared from 210 g of methyl methacrylate, 18 g of hydroxyethyl methacrylate, 72 g of ethyl acrylate and 0.5 g of isooctylmercaptopropionate in a separate reaction vessel. .

In another separate reaction vessel, methyl methacrylate (87 g), hydroxyethyl methacrylate (102 g), ethyl acrylate (102 g), methacrylic acid (9 g) and isooctyl mercaptopropionate To prepare a monomer mixture (monomer mixture B). An initiator solution was prepared from 3.8 g of VAZO-67 (DuPont) and tripropylene glycol monomethyl ether (18.7 g).

A kettle equipped with a condenser, high purity argon and monomer inlets, and a mechanical stirrer was charged with 1463 g of fluoropolymer latex. To this was added 275 g of water and 15 g of POLYSTEP B7. After initial components in the reactor and the reactor were flushed and purged for 10 minutes, 60 g of monomer mixture A was fed into the reactor at a rate of 600 g / h. Thereafter, an initiator solution was added. The components in the reactor and the reactor were stirred under argon for 30 minutes while heating to 75 占 폚. The rest of the monomer mixture A was then added at a rate of 204 g / h. After 30 minutes, the monomer mixture B was fed at a rate of 240 g / h. When all of the monomer mixture had been added, the residual monomer was consumed by maintaining the reaction temperature at 75 DEG C for an additional 30 minutes. Thereafter, 0.7 g of a mixture of t-butyl hydroperoxide and sodium formaldehyde sulfoxylate was added to the reactor and the reactor temperature was maintained at 75 C for a further 30 minutes. Then, the reaction mixture was cooled to room temperature and subjected to exhaust treatment, and the dispersion produced by the reaction was filtered through a cheese cloth. The final solids content of the dispersion was determined by gravimetric method to be 49.5 wt%. The aqueous solution was neutralized with aqueous ammonia to a pH of about 7.8. The minimum film-forming temperature of the dispersion was 15 占 폚.

The following formulation was used to prepare a two-component white water-based coating based on the above dispersion.

The A component and the final formulation were each mixed for 10 minutes at 500 rpm using a low speed mixer.

The white aqueous coating was applied to the pretreated PET and untreated PET in the same manner as in Example 1 using a 5 mil draw down blade so that the dry coating thickness was about 1 mil. These samples were flash-dried at room temperature for 10 minutes and then oven-baked at 80 ° C for 30 minutes. As in Example 1, the samples were subjected to a heat-setting test at a relative humidity of 85 DEG C / 85% for 1000 hours and a coating adhesion test. Both samples exhibited excellent adhesion maintaining 100% of the squares on the substrate as specified.

Example 18 Low-temperature bake dispersion formulation

In this preferred application, PVDF homopolymer resin formulations (as described in Example 1) were blended in a solvent suitable for coating with acrylic hybrid resins and pigments in the temperature range of 170-180 占 폚. Thereafter, the formulation of Table 22 below was prepared and then coated on a prime treated PET film (SKC SH81) with a wet thickness of 5 mil. The coating was briefly evaporated at ambient temperature for 1 minute and then baked at 170 ° C for 1 minute. The low temperature, low illumination and bake times were set to mimic the actual exposure time on a typical commercial production line. Thereafter, the dried coating was exposed to a humid heat (85 DEG C / 85%) for 1000 hours, and no adhesion failure occurred (Formulation Examples 18-1 to 18-6).

Formulations made from VF2-HFP copolymer resins were included in these examples. The copolymer resin may consist of an irregular distribution of the comonomer HFP or may be in a heterogeneous state in which the comonomer HFP is unevenly distributed in the polymer chain. In these examples, an acrylic copolymer (PARALOID B48N) resin having butyl acrylate as a comonomer was also tested.

As a comparative example, a test for a baked high boiling point solvent at a preferable low temperature and a test for a baked coating (showing embrittlement of the PET film) at a very high temperature were carried out. (Formulations 18-7 and 18-8) .

Example 19 Continuous casting equipment coating

Using the coating formulation described in Formulation Example 18-4, the coating was applied on a SKC SH 81 PET film in a continuous casting facility. The film was passed through a 12 "roll in a 10 'oven heated to 177 ° C. A coating was applied to a moving web moving at a rate of 10' per minute using a 35 trihelix gravure roller. Under conditions, a defect free dry coating having a thickness of 20 [mu] m was obtained. The coating was then subjected to wet heat exposure for 1000 hours and passed the crosshatch adhesion test.

Example 20 (Comparative) A continuous casting facility operated at a higher temperature

The coating described in Example 19 was repeated except that the oven was heated to < RTI ID = 0.0 > 190 C. < / RTI > At this temperature, the PET film contracted from an initial width of 12 "to 10 ". Also, wrinkles / warps were seen at the center cross section of the film taken from the end of the oven. When operated at 350 ^° F, the shrinkage was less than 1 "and the film was smooth.

Example 21 Using a prime treated PET substrate as an alternative

Following the formulation and coating conditions of Formulation Example 18-1, coatings were applied on commercially available PET films, Mitsubishi 4507, Toray XG232 and Kolon Astroll CI320, all of which were surface treated with acrylic primers. The coating passed the 1000 hour wet heat (85 ° C / 85%) test without any adhesive loss.

Example 22 (Comparative) Coating on unprimed PET

A coating formulation of 18-1 was used to coat the unprimed PET film (SKC SG002). After coating and exposure to wet heat, the coating failed the adhesion test at 48 hours.

Example 23 (Comparative) Coating on PET prime treated with incompatible primer

A coating formulation of 18-1 was used to coat the PET film primed with an urethane-based primer. Urethanes are less compatible with PVDF resins than PMMA-based acrylic resins. After coating, the coating failed to adhere at 24 hours after wet heat exposure.

Example 24 (Comparative) Coating on a corona-treated PET film instead of prime treatment

The unprimed PET film was subjected to high voltage corona discharge treatment. Immediately after treatment, the film was coated with PVDF dispersion formulation 18-4 and baked under the same conditions. At 48 hours of wet heat exposure, the coating failed the adhesion test.

Lamination test

To demonstrate that these coatings are suitable for solar backing sheets, several samples of coated PET films were coated on a glass substrate having a EVA (15295P EVA) bonding layer between the PET side of the coated film and the glass Substrate. Lamination was performed on a P-Energy laminator model L036A using the following process:

Step 1 - Vacuum for 10 minutes while lifting from 100 ° C to 145 ° C

Step 2 - raise to 150 ° C under pressure

Step 3 - Keep at 150 ° C for 10 minutes under pressure

Step 4 - Cool down to about 80 ° C under pressure.

Step 5 - Relieve pressure and remove sample

The film samples to be tested included samples from 18-1, 18-3, 18-4, and the coating facility implementation (Example 19). After lamination, a smooth film with minimal surface defects was formed. Visually, these laminate coatings were nearly identical to commercially available backsheet samples made by direct film lamination. These coatings passed the cross-sectional cutting adhesion test after lamination.

Weathering data

Coated PET film samples were subjected to accelerated weathering exposure tests using Xenon Arc (ASTM G155) and QUVB (ASTM G53). Color (Delta E *) and gloss changes were monitored. Typically, the high performance weather resistant fluoropolymer coating had a gloss retention of greater than 70% and a delta E * of less than 4 after 5000 hours of QUVB accelerated weathering. The results are tabulated below.

At QUVB 3000 hours, representative coatings of the present invention were well within performance targets.

Claims (11)

a. Transparent glazing external material;
b. A plurality of solar cells encapsulated and interconnected; And
c. A backsheet with a supporting substrate coated with a fluoropolymer composition on one or both sides exposed to the environment
Wherein the fluoropolymer composition comprises a low bake temperature dispersion of a non-functionalized polyvinylidene fluoride (PVDF) homopolymer or copolymer and a non-functionalized acrylic polymer, wherein the dispersion At least 40% by weight is polyvinylidene fluoride (PVDF), said dispersion being a solvent dispersion, said solvent being a hydrophobic solvent or a mixture of hydrophobic solvents, said hydrophobic solvent or mixture of hydrophobic solvents Wherein the composition comprising the low temperature baking dispersion is capable of forming a dry film at a temperature of from 170 to 180 占 폚 and wherein the fluoropolymer composition is free of crosslinking agents , Solar modules. The method of claim 1, wherein the non-functionalized acrylic polymer is selected from the group consisting of paraloids

) B44 Acrylate copolymer, photovoltaic module. The method of claim 1, wherein the fluoropolymer composition comprising a low-temperature baking dispersion of a non-functionalized polyvinylidene fluoride (PVDF) homopolymer or copolymer and a non-functionalized acrylic polymer is an acryl-modified fluoropolymer (AMF) In the form of a solar module. The photovoltaic module of claim 1, wherein the back sheet substrate is a primed or unprimed substrate. The photovoltaic module of claim 4, wherein the prime treated substrate is prime treated by corona treatment or by a coating method using an adhesive compound. The back sheet as claimed in claim 1, wherein the back sheet has the fluoropolymer composition in an outermost layer and has at least one blocking layer selected from the group consisting of ethylene vinyl acetate, polyethylene terephthalate, polypropylene terephthalate, aluminum, Further comprising a multi-layer structure. The photovoltaic module of claim 1, wherein the fluoropolymer composition further comprises at least one of from 2 to 30 weight percent of an inorganic pigment or filler. The photovoltaic module of claim 1, wherein the fluoropolymer is a polyvinylidene fluoride (PVDF) copolymer containing 1 to 29 weight percent of hexafluoropropene. The photovoltaic module of claim 1, wherein the back sheet substrate is a polyethylene terephthalate or polybutylene terephthalate substrate. The photovoltaic module of claim 1, wherein the backsheet substrate further comprises a functional polyolefin. A polymeric substrate coated with a fluoropolymer composition comprising at least one side of a non-functionalized polyvinylidene fluoride (PVDF) polymer and a low-temperature baking dispersion of a non-functionalized acrylic polymer, wherein the dispersion is a solvent-based dispersion, Wherein the solvent is a hydrophobic solvent or a mixture of hydrophobic solvents and wherein the hydrophobic solvent or mixture of hydrophobic solvents has a solubility in water at 25 DEG C of less than 10% and the composition comprising the low temperature baking dispersion is dried at a temperature of 170 to 180 DEG C Wherein the fluoropolymer composition is capable of forming a film, and wherein the fluoropolymer composition does not contain a crosslinking agent.